The present inventive concepts relate to semiconductor devices and, more particularly, to semiconductor devices having transistors capable of adjusting threshold voltage and methods for fabricating the same.
Insulated gate field effect transistors, commonly referred to as MOSFETs, include spaced apart source and drain regions and a channel region therebetween. Operation of the MOSFET is controlled by a voltage that is applied to an insulated gate on the channel region. A threshold voltage of a MOSFET is the gate voltage at which the transistor turns on.
Generally, ion implantation processes are used to adjust threshold voltages of semiconductor devices. To obtain various values of the threshold voltage in one wafer, the ion implantation process for adjustment of the threshold voltage may require a plurality of photolithography processes in proportion to the number of threshold voltages, so that cost may increase. In fully depleted devices, there may also be problems such as incomplete doping on a small dimension wafer and variation of the threshold voltage.